1. Field of the Invention
This invention relates to a molded synthetic resin surface fastener in which a substrate sheet and a multiplicity of engaging elements projecting from one surface of the substrate sheet are formed integrally with each other, and more particularly to a molded surface fastener which has adequate engaging strength and rate suitable for use in a joint of industrial materials, such as ceiling materials and wall materials, subject to peeling forces and which has adequate durability without giving damage to engaging elements of the companion surface fastener at the time of peeling.
2. Description of the Related Art
Molded surface fasteners of the described type have greater engaging strength compared to the ordinary knitted or woven surface fasteners and are therefore widely used in joining interior ornamental materials, such as wall materials and ceiling materials. Generally, the individual engaging element of the molded surface fastener has a stem standing from one surface of a substrate sheet, and a hook curving in one direction from the distal end of the stem and terminating in an end directed to the surface of the substrate sheet.
In the case that the individual engaging element of the molded surface fastener is a hooked member having the above-mentioned simple hook structure, in order to increase the degree of strength of engagement with a looped member, which is the companion engaging element, it has been customary to mold the engaging elements of rigid synthetic resin or to increase the size of the looped member. However, the rigid engaging element will give an undesirable touch and it tends to be out of engagement of the companion looped member. In the case of the large-sized looped member, it not only would become rigid but would be reduced in the number of engaging elements per unit area on the substrate sheet, thus making it difficult to secure a predetermined degree of engaging strength. If one of the hooked and looped members is increased in size, the other member of smaller size teams to be damaged when the looped member is disengaged from the hooked member.
Consequently, soft synthetic resin materials, such as polyester, polyamide and polyurethane, usually suitable for molded surface fasteners are used, and at the same time, various forms of engaging elements are put into practice in order to secure the relative strength of hooked and looped members and in order to increase the engaging strength. A typical form of engaging element, as disclosed in, for example, Japanese Patent Laid-Open Publications Nos. SHO 47-31740 and HEI 4-224703, has front and rear engaging portions symmetrically projecting from the distal end of a generally trapezoidal hook. An alternative form, as disclosed in, for example, Japanese Utility Model Laid-Open Publication No. HEI 4-128611, has front and rear hooks symmetrically branched from the distal end of a stem. According to these known forms, the number of engaging elements per unit area on the substrate sheet increases to increase the rate of engagement with companion engaging elements so that the engaging strength of the entire surface fastener is increased.
The foregoing surface fasteners for industrial materials are not subject to repeated engaging and disengaging as often as the ordinary surface fasteners for daily goods. However, if they are used in interior materials of cars, the interior material has to be peeled off the car body when the car body is inspected or repaired.
In the engaging element disclosed in each of the above-identified publications, a single looped member tends to come into engagement with the front and rear engaging portions at the same time, which is a so-called hanging engagement, so that the looped member can hardly be disengaged from the engaging portions. If the peeling of the surface fastener is forced, the looped member or engaging portion in hanging engagement would be broken and thereafter the engaging strength would be lowered.
Yet when the looped members come into engagement with at least one of the front and rear engaging portions with no banging engagement, the upward force acting on the engaging portions simply tends to act upwardly so that the engaging portion tends to be broken at its base, i.e. the joint of the engaging portion and the stem.